1. Field of the Invention
The present invention pertains to magnetically-operable control mechanisms. More specifically, the present invention relates to solenoid actuators for operating switches, valves, indicators, and the like, particularly where such devices are to be moved between one configuration and another. The present invention finds particular application in low temperature environments, for operating valves to control flow of cryogenic fluids, for example.
2. Description of Prior Art
Solenoid devices are known for selectively moving control plungers or arms to operate switches or valves in the manner of relays. A solenoid electromagnet is used to establish a magnetic field to so move the plunger or arm in one direction. In a magnetically latching solenoid an oppositely-directed magnetic field may be used to permit the return of the control mechanism to its former position. A mechanical device, such as a biasing spring, may serve to so move the control device toward its former position.
Mechanical latching mechanisms may be employed to lock the control device in position after it has been moved by an electromagnet. However, such mechanical latches may include moving parts which tends to decrease the reliability of the solenoid device. U.S. Pat. No. 3,040,217 discloses a two-position electromagnetic actuator which employs a pair of ring permanent magnets as latching devices.
U.S. Pat. No. 3,699,486 describes a relay for operation over a wide range of temperatures. Electromagnetic devices are limited in operation at cryogenic temperatures, if the resistance of their coil wiring becomes superconducting. Even if the voltage is reduced to a very low, though non-zero value, the coil circuit may draw excessive current.